The invention relates to a system and method for controlling the feeding of fiber flock to associated textile machinery in a manner in which changes in the production requirements of the machinery and fiber conditions are accounted for with minimal over or under supply of fiber.
Conventionally, fibers, particularly cotton, are opened from a bale and cleaned on machines typically called blowroom machines which open and separate the fibers for trash removal in stages. Fiber is delivered from the blowroom machines to a fine opening flock feeder and delivery system which feeds the fibers to an associated textile machine such as a card. In the card, the fibers are straightened and aligned parallel prior to being drawn off in the form of a sliver. The carded fibers can also be drawn off in the form of a non-woven fiber batt.
The flock feeder is typically connected by a pneumatic delivery system to a chute feed of the card having a vertical chute in which fibers are accumulated. In the chute feed, fibers are compressed for delivery to the card in the form of a compacted fiber batt.
The fiber flock is delivered from the flock feeder by means of a fiber-laden airflow. The fiber laden air enters the entrance of the chute feeder whereupon the fiber flock contained in the air is deposited in the shaft of the chute above a top feed roll. The top feed roll feeds the fiber flock into a formation section of the chute where the fiber flock is compressed into the fiber batt. Bottom delivery rolls convey the fiber batt to the licker end of the card. By controlling the weight of the fiber batt, a uniform sliver or non-woven fiber batt is produced by the card.
In order for the card to produce a desired output, a corresponding weight of fiber flock is supplied to the card by the chute feed in the form of fiber batt. The weight of supplied fiber flock in the batt depends on feeding conditions in the chute feed. An important feeding condition is the even distribution and level of fiber flock across the width of the chute. Even fiber distribution is a function of pressure. The pressure is determined by the quantity of fiber flock in the fiber-laden airflow coming from the air blower fed by the flock feeder in the blowroom.
There are many changing factors which influence and can cause minor deviations in the pressure of the fiber-laden airflow coming from the transport blower. First there are the conditions of the fiber flock which include degree of opening, density, resistance to the walls of the air duct, position in the duct, and temperature and humidity. These factors are constantly changing which makes control of the air pressure difficult due to the complex arrangement of the fiber flock in the airflow. Second, there may be major deviations in the pressure caused by changes in the production requirements of the card. For example, as the desired weight output of the card is varied, so must the quantity of fiber and hence pressure of the fiber-laden air if the output of the card is to be of a regular density and uniform weight.
U.S. Pat. No. 4,321,732 teaches sensing of the pressure in an air distribution conduit downstream of the blowroom transport blower. The signal representing the sensed pressure is converted into an analog signal and utilized to generate a continuous stepless electric analog signal which controls the speed of the feeding roll supplying fiber flock to the transport blower. However, the problem arises in that strict analog control of the feed roller in the proposed manner may create a condition of over supply or under supply of fiber due to the aforedescribed complex nature of the fiber-laden airflow and overresponse to changes in the factors which influence the airflow and pressure and production requirements.
U.S Pat. No. 4,535,511 teaches controlling the feed rollers of a flock feeder in response to a sensed fiber volume to prevent intermittent operation by utilizing a continuous analog control signal which gives rise to the aforesaid problems. The level of fiber flock in a chute feed is sensed as well as conditions downstream of the carding machine. The compensation of adjusting flock feed at the flock feeder in response to conditions at the end of the card are not entirely effective.
In U.S. Pat. No. 3,709,406 a desired air pressure drop is created across a fiber flock column in a chute feeder, and the pressure drop is changed in relation to deviations in the output of the card to reduce further deviations. Photocells are utilized to control the height of the fiber flock column.
Accordingly, an important object of the present invention is to control the amount of fiber flock introduced into a pneumatic delivery system in such a manner that factors which change and influence the quantity of introduced fiber are responded to without overcompensation.
Still another object of the present invention is to provide a control system and method for controlling the quantity of fiber flock introduced into a fiber delivery system in response to changes in production requirements and fiber delivery conditions in such a manner that minor transitory deviations in the sensed quantity of introduced fiber are taken into account and determined before committing the system to a permanent change in introduced fiber quantity.
Still another important object of the present invention is to provide a system and method for controlling textile fiber processing machinery that includes a pneumatic fiber delivery system into which a fiber quantity is introduced by a fiber controllable fiber input wherein the fiber input is normally controlled by an oscillating step control signal which is automatically interrupted by an integrated ramp signal when large deviations are detected which require a new input rate and minor transitory deviations are taken into account without over reaction.